Multi-camera calibration method for a vehicle moving along a vehicle assembly line

ABSTRACT

A method of calibrating cameras of a multi-camera vision system for a vehicle moving along a vehicle assembly line includes equipping the vehicle as it moves along the vehicle assembly line with a plurality of cameras and equipping the vehicle with an image processor for processing image data captured by the cameras. As the vehicle moves along the vehicle assembly line, a driver-side target at a driver-side region of the vehicle assembly line is present within the fields of view of front, driver-side and rear cameras and a passenger-side target at a passenger-side region of the vehicle assembly line is present within the fields of view of the front, passenger-side and rear cameras. The cameras are calibrated responsive to processing image data of the driver-side target captured by the front, rear and driver-side cameras and image data of the passenger-side target captured by the front, rear and passenger-side cameras.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/663,979, filed Jul. 31, 2017, now U.S. Pat. No. 10,284,818,which is a continuation of U.S. patent application Ser. No. 14/046,174,filed Oct. 4, 2013, now U.S. Pat. No. 9,723,272, which claims the filingbenefits of U.S. provisional applications, Ser. No. 61/710,924, filedOct. 8, 2012, and Ser. No. 61/710,247, filed Oct. 5, 2012, which arehereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to vision systems for vehiclesand, more particularly, to vision systems having a plurality ofexteriorly facing cameras disposed at a vehicle.

BACKGROUND OF THE INVENTION

Rear backup cameras and other exterior vision systems are known for usein vehicles. Examples of such systems are described in U.S. Pat. Nos.7,859,565; 6,611,202; 6,222,447; 5,949,331; 5,670,935 and/or 5,550,677,which are hereby incorporated herein by reference in their entireties.Such systems may display images for viewing by the driver of the vehiclethat provide a view exterior of the vehicle. It is known to provide aplurality of cameras at a vehicle, such as a forward facing camera, arearward facing camera and opposite sideward facing cameras, and tostitch together images captured by the cameras to provide a surroundview or top down view for displaying for viewing by a driver of thevehicle.

SUMMARY OF THE INVENTION

The present invention provides a means for calibrating the imagestitching of the images captured by two or more cameras of amulti-camera vision system of a vehicle.

The present invention provides a simplified calibration process thatuses multiple parallel lines with marks or tick marks for multi-cameraimage stitching calibration. The calibration system of the presentinvention may calibrate the camera and system while the vehicle ismoving along a vehicle assembly line. Special targets trigger imagecapturing while the vehicle is moving. Optionally, the calibrationsystem may utilize user actuatable inputs to provide a manualcalibration process that a user can perform while viewing displayedimages derived from image data captured by the vehicle cameras. Thecaptured image data includes areas where there are overlapping fields ofview of the cameras, with one or more targets or markings disposed atthe overlapping regions to facilitate calibration of one or more of thecameras.

These and other objects, advantages, purposes and features of thepresent invention will become apparent upon review of the followingspecification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a vehicle equipped with a multi-camera visionsystem in accordance with the present invention;

FIG. 2 is a plan view of a vehicle disposed at a calibration pattern inaccordance with the present invention;

FIGS. 3-5 are exemplary images captured by a camera and adjusted via theprocess of the present invention;

FIG. 6 is a plan view of a vehicle having its cameras calibrated inaccordance with the present invention;

FIG. 7 is a schematic of a math correction process of the presentinvention;

FIG. 8 is a schematic of the images before and after a lens-to-sensormisalignment assessment and correction process is performed inaccordance with the present invention;

FIGS. 9 and 10 are schematics of images as processed via a perspectivecorrection in accordance with the present invention;

FIGS. 11-16 are plan view of vehicles disposed at various calibrationpatterns in accordance with the present invention;

FIG. 17 are exemplary user inputs or interfaces suitable for use in themanual calibration process of the present invention;

FIG. 18 shows an image of a top down view of a vehicle beforecalibration (A) and after calibration (B) via a calibration system ofthe present invention; and

FIG. 19 is an image of a top down view of a vehicle for calibrating thecameras of the vision system via a graphic overlay means in accordancewith the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and the illustrative embodiments depictedtherein, a vehicle 10 includes an imaging system or vision system 12that includes at least one exterior facing imaging sensor or camera,such as a rearward facing imaging sensor or camera 14 a (and the systemmay optionally include multiple exterior facing imaging sensors orcameras, such as a forwardly facing camera 14 b at the front (or at thewindshield) of the vehicle, and a sidewardly/rearwardly facing camera 14c, 14 b at respective sides of the vehicle), which captures imagesexterior of the vehicle, with the camera having a lens for focusingimages at or onto an imaging array or imaging plane or imager of thecamera (FIG. 1). The vision system 12 includes a control or processor 18that is operable to process image data captured by the cameras and mayprovide displayed images at a display device 16 for viewing by thedriver of the vehicle (although shown in FIG. 1 as being part of orincorporated in or at an interior rearview mirror assembly 20 of thevehicle, the control and/or the display device may be disposed elsewhereat or in the vehicle).

The present invention provides a simplified calibration process thatuses targets or multiple parallel lines with marks or tick marks 22 formulti-camera image stitching calibration (FIG. 2). The calibrationsystem of the present invention may calibrate the camera and system(such as by adjusting the field of view of the camera or cameras oradjusting image processing of image data captured by the camera orcameras or the like to accommodate for a misalignment or degree ofmiscalibration of the camera or cameras) while the vehicle is movingalong a marked path or lane, such as along a vehicle assembly line orthe like. The cameras and the image processing of images captured by thecameras are calibrated and/or adjusted to provide an enhanced stitchedtop down display image or birds eye view of the vehicle and itssurroundings to the driver of the vehicle, as discussed below. Thesystem may utilize aspects of the systems described in InternationalPublication Nos. WO 2013/074604; WO 2012/145818 and WO 2012/145822,which are hereby incorporated herein by reference in their entireties.

Multi-camera Stitching Calibration:

The stitching calibration process is described below:

The process provides a math model oriented, multi-target based nominaladjustment, where:

-   -   the math model fully characterizes lens distortion and camera        mounting positions;    -   the math model provides for multi-axis dewarping and perspective        change;    -   multiple targets, targets coverage at stitching corners and        camera front center;    -   camera multi-axial (pitch, yaw and roll) deviation measurement        by feature patterns on targets; and    -   camera lens-imager misalignment measurement by feature patterns        on targets.

The system uses the above math models to compute needed angle changesand pixel shifts. A final and minor pixel “nudging” to fine tune fieldmis-match due to lens deviation from a lens model (distortion curvedeviation and cylindrical asymmetricity) is done via controlled andlocalized movement of group pixels around a stitching border area toachieve sufficient stitching performance.

The calibration of a single camera in accordance with the presentinvention may utilize the following steps (and with reference to FIGS.3-5):

-   -   Dewarp (flatten) image;    -   Utilize feature patterns on center targets to calculate        lens-imager mis-alignment;    -   Utilize feature patterns on corner and center targets to        calculate angle (pitch, yaw and roll) values to rotate;    -   Compensate for camera mounting deviation from nominal angles;        and    -   Utilize perspective remapping and scaling to achieve birds-eye        view.

The calibration for multi-camera stitching in accordance with thepresent invention may utilize the following steps (and with reference toFIG. 6):

-   -   Merge multiple images to a single birds-eye view;    -   Use target signature patterns in overlapped area to measure        mis-matching distances between the same signature patterns of        two adjacent cameras; and    -   Determine if a larger (greater than a threshold level) mis-match        exists;    -   If a threshold level (or greater than a threshold level) or        degree of mis-match exists, move, stretch and/or rotate the        whole camera image to achieve an acceptable or within tolerances        or thresholds match;    -   If only a small mis-match (less than the threshold level)        exists, stretch and move (nudge) pixels in the overlap area of        adjacent camera images to achieve smooth stitching.

The above large pixel movement or pixel “nudge” should be within definedranges. If the movement or nudge exceed the defined ranges, the systemmay run another iteration of single camera calibration and multi-cameramatching.

Correction Steps Outline:

Step 1: Math model by pre-programmed Look-up Table or math formulas(with reference to FIG. 7):

-   -   Math model fully transform/corrects lens distortion based on        lens nominal design data;    -   Math model adjusts all four (4) virtual camera positions to a        vertical orientation over a selected floor location based on        nominal vehicle CAD to achieve properly scaled top-down scenes;    -   Results will reveal some imperfections based on some physical        rotation and translation errors common in a real-world        environment;    -   Some distortion correction errors may be evident if the lens        warp center is not at image center;    -   Lens distortion tolerance may be considered negligible and may        not be measured or corrected for;    -   The resulting image or images (at the “After math correction”        portion of FIG. 7) will better facilitate target finding        algorithms.

Step 2: Lens-to-Sensor Misalignment Assessment and Correction (withreference to FIG. 8):

-   -   The lens-to-sensor misalignment results in a mismatch between        the warp center of the lens or lenses and algorithm's dewarp        center. This mismatch results in a predictable curvature of the        scene which should otherwise be flat. In general, vertical        misalignment will primarily result in curved horizontal lines        while horizontal misalignment will yield curved vertical lines.    -   This curvature is much more apparent when there is a vertical        misalignment vs. horizontal for this type of application. The        reason is that the actual positions of the cameras relative to        the area to be seen necessitates more vertical image stretching.        This amplifies the curvature of horizontal lines while        diminishing the curvature of vertical lines. Furthermore, the        areas to be seen in the final top-view scene show more image        width than height (reference four windows for each camera). This        makes the curvature of a horizontal line much more apparent.    -   The camera assembly systems with reasonable active        lens-to-sensor alignment capabilities will reduce tolerances        enough for horizontal misalignment to be ignored. Only        horizontal target line curvatures need to be assessed to        calculate and correct for vertical error.    -   The relationship between the degree of curvature of horizontal        lines and vertical misalignment of lens to imager centers can be        established by a set of math formulas or a look-up-table. The        degree of curvature of horizontal lines can be measured by        detecting edges and points of the target patterns. Thus, the        vertical misalignment of an individual camera already mounted on        the vehicle can be readily measured by the degree of horizontal        lines of the target. The method of the present invention is        especially advantageous for systems where there is no data        communication between the cameras and the processing ECU, such        that ECU cannot read each individual camera's “intrinsic        parameters”, which include the vertical misalignment of the lens        to the imager center. The “intrinsic parameters” of each camera        can be measured individually at the camera manufacturing and        testing places and can be stored in non-volatile memory, such as        EEPROM and flash memory. However, for the lower cost cameras and        systems where “intrinsic parameters” cannot be saved or        communicated to ECU, the only method to correct for the image        distortion caused by misalignment of the lens to the imager        center is to measure the misalignment during stitching        calibration onsite at the vehicle assembly plant or service        center. The above described method performs such a misalignment        and compensation process.

Step 3: Perspective Correction (with reference to FIGS. 9 and 10):

-   -   Once all lines are straight, the remaining rotation and        translation errors can be solved for so that perspective        correction can be achieved by adjusting the virtual camera        positions. A math model of homographic transformation        represented by a 3×3 matrix is used to perform the perspective        corrections. Other math models may be used to achieve similar        perspective effects.    -   Aspect changes may be needed as well to better fit the final        scene. The homographic transformation math model can fulfill the        aspect change as well as the part of perspective correction.

Step 4: Pixel Nudge (fine tune):

-   -   Determine if large mis-matches (or greater than threshold level        mis-matches) exist at overlap areas:        -   if yes, repeat steps 2 and 3.        -   If only small mis-match (less than threshold level), stretch            and move (nudge) pixels in overlap area of adjacent camera            images to achieve smooth stitching for displayed image.

The system of the present invention may utilize any suitable frame ofreference at or near the vehicle for the vehicle to utilize a known orexpected pattern or target to determine the calibration of the camerasand system. For example, and with reference to FIGS. 2 and 11-16,suitable target types may include a chess board pattern, continuous ordiscretely placed, parallel lines (two or more lines at each side of thevehicle), parallel lines with tick marks (such as tick marks or shortmarks that intersect the parallel lines at an angle, such as at 90degrees relative to the parallel lines), parallel lines both verticaland horizontal, and/or added special patterns, dots, colors forhomographic process and calibration triggering.

Vehicle Assembly Line Calibration With Vehicle Moving With ConveyerLine:

The present invention may use the following technique to calibratemulti-camera systems in a vehicle assembly line. For example, two ormore straight lines may be placed at both sides of a vehicle conveyer ofthe assembly line (such as at or near the end of the assembly line).Multiple tick marks or horizontal short lines may be disposed at orplaced on top of the longer straight lines that extend along theconveyor path. The vertical lines are long enough and spaced wide enoughapart from the vehicle to cover an area that is required to calibratemulti-camera stitching. The tick marks or shorter lines or markings areplaced at or near the corner areas of the vehicle where the adjacentcameras have overlapping fields of view on the ground.

When a vehicle is moved on a conveyer or a flat bed and into thecalibration area, the multi-camera system is powered on and in the modeof waiting for trigger of picture acquisition or image capture. Someobjects with special or particular shapes, colors, and/or patterns areplaced at locations at the side of the conveyer, either on the ground orabove ground. The objects are designed to be easily recognized andtracked in the camera images by an image processing unit (such as animage processor inside or part of the camera or an image processor in orpart of a multi-camera processing unit). Once the vehicle is moved to adesired position, and the objects in the camera image reach thepredefined locations, the processing unit will trigger an event that allthe cameras will simultaneously acquire and store the images for thefollowing stitching calibration computation. The stitching calibrationprocess may be the same as the stitching calibration process done in astatic fashion, such as described above.

Manual Stitching Calibration:

Using the techniques described above or by other suitable means ormethods, the vision system or cameras of a vehicle coming out of avehicle assembly plant may be calibrated or adjusted with suitablestitching performance. However, when the vehicle is involved in somekind of accident or other circumstances and needs a repair, such as whenone or more cameras of a multi camera system is replaced on the vehicle,due to the variation or tolerance of the new camera(s) installation interms of camera angles, the original stitching may no longer provideproper performance. In an automotive service center where the repairtakes place, the environment in the shop floor may not be the same asthe assembly plant and may have variations in lighting, space, groundevenness and/or the like. On the other hand, unlike in an assembly plantwhere the time of calibration for each vehicle is limited, in a servicecenter, the technician has more time to calibrate a multi camerastitching than what's available in an assembly plant. Besides thepossibility of using the same automatic calibration target and processas described above, one can use a manual calibration process thatinvolves the adjustment and judgment of a human. The calibrationinvolves human machine interface, such as a video display screen and/orone or more or several buttons or touch sensors or inputs or the like onthe display touch panel, or if touch panel is not available, an externaldevice that has buttons or inputs or sensors and connects to vehiclecommunication bus, or existing vehicle switches, dials, buttons,steering wheel or pedals or any other suitable user input.

Optionally, the calibration process can use any of the calibrationtargets described above (and such as shown in FIGS. 2 and 11-16).

Manual Calibration Control Interface:

The manual stitching calibration system or process of the presentinvention requires a human machine interface (HMI) which allows the userto view the real time image and judge the degree of stitching needed toprovide the desired display image or images, and to control andmanipulate the individual camera image or images. One or multipletargets may be disposed at or laid on the ground around the vehicle,with the patterns (such as lines, squares and/or the like) in the targetassisting the user to judge the performance of stitching calibration.

Video Display

The video display in the vehicle, which displays the video output from amulti camera ECU can be used as the video display device. An externalvideo monitor that connects to the video output of the ECU mayoptionally be used as the display device if it is required or desiredfor convenience or any other reasons. This external monitor can be ahandhold video monitor, a video projector, a video monitor on a rollingcart, or a video display in one's eye glasses or any other suitabledisplay device. The video monitor can have built-in graphic overlaypatterns that can be used to assist the technician to perform thestitching calibration, such as like guiding the positioning of groundtargets or the like.

Controller

The controller is a device that allows the user to enter commands tomanipulate the camera images and to select one or more cameras or otheractivities during the stitching calibration process. The controller isconnected to the multi-camera ECU, such as via a direct communicationchannel or via a vehicle bus. The following forms of controllers aresuitable for use in the system of the present invention.

The controller may comprise or may be responsive to a touch panel of thevideo monitor that displays real time video. The buttons or sensors orinputs of or on the touch panel allow the user to manipulate images andperform the calibration. The communication of button status and commandsmay be through an internal vehicle bus network to which the videodisplay and multi-camera ECU are both connected.

The controller may comprise a handheld device that connects to thevehicle bus network through a special port in vehicle. For example, ahandheld device used commonly in a vehicle service center can beprogrammed to add and serve the stitching calibration purpose.

Using an existing control mechanism of the vehicle, for example, thebuttons, dials and even steering wheel and pedals of the vehicle mayalso or otherwise be used while remaining within the spirit and scope ofthe present invention. Those existing mechanisms include and may not belimited to: cruise control buttons or inputs, radio control buttons orinputs, heat and A/C control buttons or dials or inputs, light switches,windshield wiper control dials or buttons or inputs, the vehiclesteering wheel, the brake and/or gas pedal and/or the like. Using theseexisting control mechanisms in the vehicle during service centercalibration allows the vehicle manufacturers to save the cost ofdesigning and providing a separate control device and deploying such adevice to thousands of dealer service centers.

Buttons to Manipulate Image:

The buttons or user inputs that the user can use during the manualcalibration may include, but may not be limited to, the following:

-   -   Horizontal corner stretching and compression    -   Vertical corner stretching and compression    -   Horizontal stretching and compression    -   Vertical stretching and compression    -   Rotation—clockwise and counterclockwise    -   Horizontal shift    -   Vertical shift    -   Camera selection    -   Start and stop as optional

Examples of touch panel on screen buttons or inputs or sensors are shownin FIG. 17. The images of those buttons or their deviations may also beshown on the screen even when an external device or existing mechanismor mechanisms of the vehicle are used. When an external button is pushedor toggled or actuated or another form of user input is pushed ortoggled or actuated, a corresponding button or icon on the video screenmay be highlighted and thus may signal to the user that this is selectedinput and action. The on screen buttons or icons or inputs may bedisplayed in an overlay graph and may have a semi-transparent nature.

Manual Calibration Process:

One Camera Calibration:

When only one camera needs to be calibrated, the technician can use thetwo adjacent cameras, which are still in good stitching status, as thecalibration reference. The goal of the calibration process and the wayto judge a good calibration is to manipulate the image of the camerabeing calibrated such that the patterns at the border match and smoothlytransition between the good camera and the camera being calibrated.Also, when the camera is properly calibrated, the straight lines of thetarget will appear straight and the rectangles or squares of the targetwill be in their right shapes and scales.

As an example, and with reference to FIG. 18, image (A), the right sidecamera in a four camera system is out of calibration. The line patternon the ground appears in the image as mismatched or not properlycalibrated in the right side camera section. By manually rotating,stretching, and shifting the image, such as by using the appropriatepush buttons or toggle buttons or user inputs, a user or technician canrestore the left side camera image to a smoothly stitched with adjacentimage sections, such as illustrated in image (B). This process ofstitching calibration is based on direct human adjustment and judgment.It may take longer than the automatic stitching calibration describedabove, but it is suitable for use in an automotive service center wherethe conditions for automatic stitching calibration may not be feasibleor met, due to, for example, improper lighting, inadequate space, and/orthe like. On the other hand, a service center allows more time than anassembly plant for a technician to calibrate a multi camera stitching.

Target Overlay:

Optionally, and as a tool to assist manual calibration process, themulti-camera ECU may be operable to generate an overlay pattern on theoutput image or displayed image. The overlay provides guidance to theperson who is performing the calibration to position the target ortargets at the ground around or by the vehicle to a proper and accuratelocation and angle relative to the vehicle. As an example, the crosses24 shown in FIG. 19 (which may be colored or otherwise highlighted so asto be readily visible by the user during the calibration process) areoverlay patterns that should (when the cameras are calibrated) overlapwith the crossing points of horizontal and vertical lines of targets.The technician can use the overlay graph to move the target on theground to the correct positions.

Two Cameras Calibration:

When two cameras need to be calibrated, and the two cameras are notadjacent to each other, the two other cameras can be used as calibrationreferences. The process of calibration is to calibrate one camera at atime until both cameras are calibrated.

When the two cameras are adjacent one another and need to be calibrated,one can calibrate the one in the front or rear of the vehicle first,since the field of view of the front or rear camera is typically smallerthan the field of view of either of the side cameras and thus easier tojudge the deviation of target lines from the camera's calibrated stateand from the adjacent good (calibrated) camera that can be served as thereference. As a main criteria, the lines should appear as straight andthe rectangles or squares should appear in their right shapes andscales. At the border with the already calibrated camera, the patternsshall transition smoothly and continuously across the border oroverlapping areas of the images. After the first camera is manipulatedto reach the satisfactory state, one can use this first calibratedcamera and the other already calibrated camera as calibration referencesfor the second camera calibration. The calibration process for eachcamera may be similar to the single calibration process described above.After an initial calibration of the cameras, there may be the need torun another iteration of calibrating the first camera and then thesecond camera, since the first camera may not be calibrated properly viathe initial calibration and this may be more evident when it is betweentwo adjacent calibrated cameras. After the two cameras have run throughthe first pass of calibration, one can have a better view of how thewhole birds eye view stitching performance looks and do some fine tuningof the two camera calibrations.

Three Camera Calibration:

When three of the four cameras of a multi-camera system are in need ofcalibration, one should first calibrate the camera adjacent to theremaining already calibrated camera for using the calibrated camera asthe reference. As a main criteria, the lines shall appear as straightand the rectangles or square appear in their right shapes and scales. Atthe border with the already calibrated camera, the patterns shalltransit smoothly and continuously across. When the first camera iscalibrated, one can then follow the process described above forcalibrating two adjacent cameras to perform calibration to the remainingtwo cameras. As in the process of calibrating two adjacent cameras, onemight need to run another iteration to fine tune the camera manipulationof each of the three cameras to reach an optimized overall stitchingcalibration.

Four Camera Calibration:

When all four cameras are in need of stitching calibration, one maycalibrate the front or rear camera first. The criteria are to manipulatethe camera image so that the target lines appear straight and therectangles or squares appear in their right shapes and scales. Thehorizontal lines appear level in the image to compensate for any camerarotation. One can use the calibration target pattern overlay describedin the overlay section to judge the levelness of horizontal lines. Oncethe first camera is calibrated or roughly calibrated, one can follow thethree camera calibration process described above to calibrate theremaining three cameras. One or more additional iterations of thecalibration process may be performed to fine tune the cameramanipulation of each of the four cameras to reach an optimized overallstitching calibration.

Therefore, the present invention provides a calibration process formanually and/or automatically calibrating one or more or all of thecameras of a multi-camera vision system of a vehicle. For example, thepresent invention provides a calibration process for calibrating thefront, rear and driver side and passenger side cameras for a surroundview or top-down view vision system of a vehicle.

Optionally, the vision system (utilizing the forward facing camera and arearward facing camera and other cameras disposed at the vehicle withexterior fields of view) may be part of or may provide a display of atop-down view or birds-eye view system of the vehicle or a surround viewat the vehicle, such as by utilizing aspects of the vision systemsdescribed International Publication Nos. WO 2010/099416; WO 2011/028686;WO 2012/075250; WO 2013/019795; WO 2012-075250; WO 2012/154919; WO2012/0116043; WO 2012/0145501 and/or WO 2012/0145313, and/or PCTApplication No. PCT/CA2012/000378, filed Apr. 25, 2012, and publishedNov. 1, 2012 as International PCT Publication No. WO 2012/145822, and/orPCT Application No. PCT/US2012/066571, filed Nov. 27, 2012, andpublished Jun. 6, 2013 as International PCT Publication No. WO2013/081985, and/or PCT Application No. PCT/US2012/068331, filed Dec. 7,2012, and published Jun. 13, 2013 as International PCT Publication No.WO 2013/086249, and/or PCT Application No. PCT/US2013/022119, filed Jan.18, 2013, and published Jul. 25, 2013 as International PCT PublicationNo. WO 2013/109869, and/or U.S. patent application Ser. No. 13/333,337,filed Dec. 21, 2011, now U.S. Pat. No. 9,264,672, which are herebyincorporated herein by reference in their entireties.

The image processing and algorithmic processing may comprise anysuitable means for processing the images and/or image data. For example,the vision system and/or processing may utilize aspects described inU.S. Pat. Nos. 7,005,974; 5,760,962; 5,877,897; 5,796,094; 5,949,331;6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202;6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452;6,822,563; 6,891,563; 6,946,978; 7,859,565; 5,550,677; 5,670,935;6,636,258; 7,145,519; 7,161,616; 7,230,640; 7,248,283; 7,295,229;7,301,466; 7,592,928; 7,881,496; 7,720,580; 7,038,577; 6,882,287;5,929,786 and/or 5,786,772, and/or International Publication Nos. 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No. 61/838,619, filed Jun.24, 2013; Ser. No. 61/838,621, filed Jun. 24, 2013; Ser. No. 61/837,955,filed Jun. 21, 2013; Ser. No. 61/836,900, filed Jun. 19, 2013; Ser. No.61/836,380, filed Jun. 18, 2013; Ser. No. 61/834,129, filed Jun. 12,2013; Ser. No. 61/834,128, filed Jun. 12, 2013; Ser. No. 61/833,080,filed Jun. 10, 2013; Ser. No. 61/830,375, filed Jun. 3, 2013; Ser. No.61/830,377, filed Jun. 3, 2013; Ser. No. 61/825,752, filed May 21, 2013;Ser. No. 61/825,753, filed May 21, 2013; Ser. No. 61/823,648, filed May15, 2013; Ser. No. 61/823,644, filed May 15, 2013; Ser. No. 61/821,922,filed May 10, 2013; Ser. No. 61/819,835, filed May 6, 2013; Ser. No.61/819,033, filed May 3, 2013; Ser. No. 61/16,956, filed Apr. 29, 2013;Ser. No. 61/815,044, filed Apr. 23, 2013; Ser. No. 61/814,533, filedApr. 22, 2013; Ser. No. 61/813,361, filed Apr. 18, 2013; Ser. No.61/840,407, filed Apr. 10, 2013; Ser. No. 61/808,930, filed Apr. 5,2013; Ser. No. 61/807,050, filed Apr. 1, 2013; Ser. No. 61/806,674,filed Mar. 29, 2013; Ser. No. 61/806,673, filed Mar. 29, 2013; Ser. No.61/804,786, filed Mar. 25, 2013; Ser. No. 61/793,592, filed Mar. 15,2013; Ser. No. 61/793,614, filed Mar. 15, 2013; Ser. No. 61/772,015,filed Mar. 4, 2013; Ser. No. 61/772,014, filed Mar. 4, 2013; Ser. No.61/770,051, filed Feb. 27, 2013; Ser. No. 61/770,048, filed Feb. 27,2013; Ser. No. 61/766,883, filed Feb. 20, 2013; Ser. No. 61/760,366,filed Feb. 4, 2013; Ser. No. 61/760,364, filed Feb. 4, 2013; Ser. No.61/758,537, filed Jan. 30, 2013; Ser. No. 61/756,832, filed Jan. 25,2013; Ser. No. 61/754,804, filed Jan. 21, 2013; Ser. No. 61/745,925,filed Dec. 26, 2012; Ser. No. 61/745,864, filed Dec. 26, 2012; Ser. No.61/736,104, filed Dec. 12, 2012; Ser. No. 61/736,103, filed Dec. 12,2012; Ser. No. 61/735,314, filed Dec. 10, 2012; Ser. No. 61/734,457,filed Dec. 7, 2012; Ser. No. 61/733,598, filed Dec. 5, 2012; Ser. No.61/733,093, filed Dec. 4, 2012; Ser. No. 61/727,912, filed Nov. 19,2012; Ser. No. 61/727,911, filed Nov. 19, 2012; Ser. No. 61/727,910,filed Nov. 19, 2012; Ser. No. 61/718,382, filed Oct. 25, 2012; and/orSer. No. 61/713,772, filed Oct. 15, 2012, which are all herebyincorporated herein by reference in their entireties. The system maycommunicate with other communication systems via any suitable means,such as by utilizing aspects of the systems described in InternationalPublication No. WO 2013/043661, PCT Application No. PCT/US10/038477,filed Jun. 14, 2010, and/or PCT Application No. PCT/US2012/066571, filedNov. 27, 2012, and published Jun. 6, 2013 as International PCTPublication No. WO 2013/081985, and/or U.S. patent application Ser. No.13/202,005, filed Aug. 17, 2011, now U.S. Pat. No. 9,126,525, which arehereby incorporated herein by reference in their entireties.

Typically, a rearward facing camera for a rear vision system or backupassist system is activated responsive to the driver of the equippedvehicle shifting the gear actuator into a reverse gear position, wherebyvideo images captured by the camera are displayed at the video displayscreen. When the reversing maneuver is completed, such as when thedriver of the vehicle finally shifts the gear actuator out of thereverse gear position (and into either a park or neutral position or aforward gear position), display of the images captured by the cameraceases and the camera is often deactivated. The vision display systemmay operate to display the rearward images at the video mirror displayresponsive to the driver of the vehicle shifting the vehicle into areverse gear such as by utilizing aspects of the vision systemsdescribed in U.S. Pat. Nos. U.S. Pat. Nos. 5,550,677; 5,670,935;6,498,620; 6,222,447 and/or 5,949,331, and/or PCT Application No.PCT/US2011/056295, filed Oct. 14, 2011 and published Apr. 19, 2012 asInternational Publication No. WO 2012/051500, and/or U.S. patentapplication Ser. No. 13/333,337, filed Dec. 21, 2011, now U.S. Pat. No.9,264,672, which are hereby incorporated herein by reference in theirentireties.

The rearward facing camera or camera module may comprise any suitablecamera or imaging sensor, and may utilize aspects of the cameras orsensors described in U.S. Pat. Nos. 7,965,336 and/or 7,480,149, and/orU.S. patent application Ser. No. 12/091,359, filed Apr. 24, 2008 andpublished Oct. 1, 2009 as U.S. Publication No. US-2009-0244361, whichare hereby incorporated herein by reference in their entireties. Theimaging array sensor may comprise any suitable sensor, and may utilizevarious imaging sensors or imaging array sensors or cameras or the like,such as a CMOS imaging array sensor, a CCD sensor or other sensors orthe like, such as the types described in U.S. Pat. Nos. 5,550,677;5,670,935; 5,760,962; 5,715,093; 5,877,897; 6,922,292; 6,757,109;6,717,610; 6,590,719; 6,201,642; 6,498,620; 5,796,094; 6,097,023;6,320,176; 6,559,435; 6,831,261; 6,806,452; 6,396,397; 6,822,563;6,946,978; 7,720,580; 7,965,336; 7,339,149; 7,038,577 and 7,004,606;and/or PCT Application No. PCT/US2008/076022, filed Sep. 11, 2008 andpublished Mar. 19, 2009 as International Publication No. WO 2009/036176,and/or PCT Application No. PCT/US2008/078700, filed Oct. 3, 2008 andpublished Apr. 9, 2009 as International Publication No. WO 2009/046268,which are all hereby incorporated herein by reference in theirentireties.

Optionally, the exterior facing camera or cameras (such as, for example,the forward facing camera and/or the rearward facing camera and/or thesideward facing cameras) may have a wide angle rearward field of view,such as a wide angle rearward field of view that encompasses about 185degrees (fields of view larger and smaller than this may be contemplatedwhile remaining within the spirit and scope of the present invention).Thus, during a reversing maneuver, the rearward facing camera and videoprocessor and video display screen can operate to display entire images(or substantially entire images) captured by the rearward facing camera(such as, for example, images encompassed by the about 185 degree fieldof view of the camera), in order to provide video images to the driverof the vehicle of a wide area or region or blind zone immediatelyrearward of the vehicle to assist the driver of the vehicle in makingthe reversing maneuver. The rearward facing camera and/or videoprocessor and/or video display screen and/or backup assist system mayutilize aspects of the systems described in U.S. Pat. Nos. 5,550,677;5,760,962; 5,670,935; 6,201,642; 6,396,397; 6,498,620; 6,717,610;6,757,109; 7,005,974 and/or 7,265,656, which are hereby incorporatedherein by reference in their entireties.

The camera module and circuit chip or board and imaging sensor andprocessor may be implemented and operated in connection with variousvehicular vision-based systems, and/or may be operable utilizing theprinciples of such other vehicular systems, such as a vehicle headlampcontrol system, such as the type disclosed in U.S. Pat. Nos. 5,796,094;6,097,023; 6,320,176; 6,559,435; 6,831,261; 7,004,606; 7,339,149 and/or7,526,103, which are all hereby incorporated herein by reference intheir entireties, a rain sensor, such as the types disclosed in commonlyassigned U.S. Pat. Nos. 6,353,392; 6,313,454; 6,320,176 and/or7,480,149, which are hereby incorporated herein by reference in theirentireties, a vehicle vision system, such as a forwardly, sidewardly orrearwardly directed vehicle vision system utilizing principles disclosedin U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962; 5,877,897; 5,949,331;6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202;6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452;6,822,563; 6,891,563; 6,946,978 and/or 7,859,565, which are all herebyincorporated herein by reference in their entireties, a trailer hitchingaid or tow check system, such as the type disclosed in U.S. Pat. No.7,005,974, which is hereby incorporated herein by reference in itsentirety, a reverse or sideward imaging system, such as for a lanechange assistance system or lane departure warning system or for a blindspot or object detection system, such as imaging or detection systems ofthe types disclosed in U.S. Pat. Nos. 7,881,496; 7,720,580; 7,038,577;5,929,786 and/or 5,786,772, and/or U.S. provisional application Ser. No.60/618,686, filed Oct. 14, 2004, which are hereby incorporated herein byreference in their entireties, a video device for internal cabinsurveillance and/or video telephone function, such as disclosed in U.S.Pat. Nos. 5,760,962; 5,877,897; 6,690,268 and/or 7,370,983, and/or U.S.patent application Ser. No. 10/538,724, filed Jun. 13, 2005 andpublished Mar. 9, 2006 as U.S. Publication No. US-2006-0050018, whichare hereby incorporated herein by reference in their entireties, atraffic sign recognition system, a system for determining a distance toa leading or trailing vehicle or object, such as a system utilizing theprinciples disclosed in U.S. Pat. Nos. 6,396,397 and/or 7,123,168, whichare hereby incorporated herein by reference in their entireties, and/orthe like.

Optionally, the circuit board or chip (such as of the display or camerasystem or image processor or the like) may include circuitry for theimaging array sensor and or other electronic accessories or features,such as by utilizing compass-on-a-chip or EC driver-on-a-chip technologyand aspects such as described in U.S. Pat. No. 7,255,451 and/or U.S.Pat. No. 7,480,149; and/or U.S. patent applications, Ser. No.11/226,628, filed Sep. 14, 2005 and published Mar. 23, 2006 as U.S.Publication No. US-2006-0061008, and/or Ser. No. 12/578,732, filed Oct.14, 2009, now U.S. Pat. No. 9,487,144, which are hereby incorporatedherein by reference in their entireties.

The display is operable to display the captured rearward images and maycomprise a video display and may utilize aspects of the video displaydevices or modules described in U.S. Pat. Nos. 6,690,268; 7,184,190;7,274,501; 7,370,983; 7,446,650 and/or 7,855,755, and/or U.S. patentapplication Ser. No. 10/538,724, filed Jun. 13, 2005 and published Mar.9, 2006 as U.S. Publication No. US-2006-0050018, which are all herebyincorporated herein by reference in their entireties. The video displaymay be operable to display images captured by one or more imagingsensors or cameras at the vehicle. The imaging device and control andimage processor and any associated illumination source, if applicable,may comprise any suitable components, and may utilize aspects of thecameras and vision systems described in U.S. Pat. Nos. 5,550,677;5,877,897; 6,498,620; 5,670,935; 5,796,094; 6,396,397; 6,806,452;6,690,268; 6,198,409; 7,005,974; 7,123,168; 7,004,606; 6,946,978;7,038,577; 6,353,392; 6,320,176; 6,313,454 and 6,824,281, which are allhereby incorporated herein by reference in their entireties.

The video display screen may disposed at an interior rearview mirrorassembly of the vehicle (such as in a mirror casing and behind areflective element of a mirror assembly such that displayed informationis viewable through the reflective element of the mirror assembly). Theinterior mirror assembly may comprise an electro-optic reflectiveelement, such as an electrochromic reflective element, having atransflective mirror reflector (such as one or more thin metallic filmsor coatings disposed on a surface of a substrate of the reflectiveelement, such as disposed on the front surface of the rear substrate,commonly referred to as the third surface of the mirror reflectiveelement) that is partially transmissive of visible light therethroughand partially reflectant of visible light incident thereon, such as amirror reflective element of the types described in U.S. Pat. Nos.7,274,501; 7,255,451; 7,195,381; 7,184,190; 5,668,663; 5,724,187 and/or6,690,268, which are all hereby incorporated herein by reference intheir entireties). Thus, the video display screen, when operating todisplay video images or the like, is viewable through the transflectivemirror reflector and the mirror reflective element by the driver of thevehicle and, when the video display screen is not operating to displayvideo images or the like, the video display screen is not readilyviewable or observable or discernible to the driver of the vehicle, suchthat the presence of the video display screen is rendered covert by thetransflective mirror reflector and the driver of the vehicle normallyviews the mirror reflector and reflective element to view the reflectedrearward image at the mirror reflective element. Optionally, the videodisplay screen may be disposed elsewhere in the vehicle, such as at orin an accessory module or windshield electronics module or overheadconsole or center stack region of the instrument panel or elsewhere atthe instrument panel or other areas of the vehicle, while remainingwithin the spirit and scope of the present invention.

Optionally, the mirror assembly may include one or more displays, suchas the types disclosed in U.S. Pat. Nos. 5,530,240 and/or 6,329,925,which are hereby incorporated herein by reference in their entireties,and/or display-on-demand transflective type displays, such as the typesdisclosed in U.S. Pat. Nos. 7,855,755; 7,626,749; 7,581,859; 7,338,177;7,274,501; 7,255,451; 7,195,381; 7,184,190; 5,668,663; 5,724,187 and/or6,690,268, and/or in U.S. patent applications, Ser. No. 11/226,628,filed Sep. 14, 2005 and published Mar. 23, 2006 as U.S. Publication No.US-2006-0061008; and/or Ser. No. 10/538,724, filed Jun. 13, 2005 andpublished Mar. 9, 2006 as U.S. Publication No. US-2006-0050018, whichare all hereby incorporated herein by reference in their entireties, sothat the displays are viewable through the reflective element, while thedisplay area still functions to substantially reflect light, in order toprovide a generally uniform prismatic reflective element even in theareas that have display elements positioned behind the reflectiveelement. The thicknesses and materials of the coatings on thesubstrates, such as on the third surface of the reflective elementassembly, may be selected to provide a desired color or tint to themirror reflective element, such as a blue colored reflector, such as isknown in the art and such as described in U.S. Pat. Nos. 5,910,854;6,420,036 and/or 7,274,501, which are all hereby incorporated herein byreference in their entireties.

Optionally, the vehicle may include one or more other accessories at orwithin the mirror assembly or otherwise associated with or near themirror assembly, such as one or more electrical or electronic devices oraccessories, such as a blind spot detection system, such as disclosed inU.S. Pat. Nos. 5,929,786; 8,058,977; 5,786,772; 7,720,580; 7,492,281;7,038,577 and 6,882,287, a communication module, such as disclosed inU.S. Pat. No. 5,798,688, a voice recorder, microphones, such asdisclosed in U.S. Pat. Nos. 7,657,052; 6,243,003; 6,278,377 and/or6,420,975, speakers, antennas, including global positioning system (GPS)or cellular phone antennas, such as disclosed in U.S. Pat. No.5,971,552, transmitters and/or receivers, such as a garage door openeror the like or a vehicle door unlocking system or the like (such as aremote keyless entry system), a digital network, such as described inU.S. Pat. No. 5,798,575, a high/low headlamp controller, such as acamera-based headlamp control, such as disclosed in U.S. Pat. Nos.5,796,094 and/or 5,715,093 and/or U.S. patent application Ser. No.12/781,119, filed May 17, 2010 and published Nov. 17, 2011 as U.S.Publication No. US 2011-0280026, a memory mirror system, such asdisclosed in U.S. Pat. No. 5,796,176, a hands-free phone attachment, avideo device for internal cabin surveillance and/or video telephonefunction, such as disclosed in U.S. Pat. Nos. 5,760,962 and/or5,877,897, a remote keyless entry receiver, lights, such as map readinglights or one or more other lights or illumination sources, such asdisclosed in U.S. Pat. Nos. 6,690,268; 5,938,321; 5,813,745; 5,820,245;5,673,994; 5,649,756; 5,178,448; 5,671,996; 4,646,210; 4,733,336;4,807,096; 6,042,253; 5,669,698; 7,195,381; 6,971,775 and/or 7,249,860,an imaging system or components or circuitry or display thereof, such asan imaging and/or display system of the types described in U.S. Pat.Nos. 7,881,496; 7,526,103; 7,400,435; 6,690,268 and 6,847,487, and/orU.S. patent applications Ser. No. 12/578,732, filed Oct. 14, 2009, nowU.S. Pat. No. 9,487,144; and/or Ser. No. 12/508,840, filed Jul. 24, 2009and published Jan. 28, 2010 as U.S. Publication No. US 2010-0020170, analert system, such as an alert system of the types described in PCTApplication No. PCT/US2010/25545, filed Feb. 26, 2010 and published Sep.2, 2010 as International Publication No. WO 2010/099416, a video devicefor internal cabin surveillance (such as for sleep detection or driverdrowsiness detection or the like) and/or video telephone function, suchas disclosed in U.S. Pat. Nos. 5,760,962 and/or 5,877,897, a remotekeyless entry receiver, a seat occupancy detector, a remote startercontrol, a yaw sensor, a clock, a carbon monoxide detector, statusdisplays, such as displays that display a status of a door of thevehicle, a transmission selection (4wd/2wd or traction control (TCS) orthe like), an antilock braking system, a road condition (that may warnthe driver of icy road conditions) and/or the like, a trip computer, atire pressure monitoring system (TPMS) receiver (such as described inU.S. Pat. Nos. 6,124,647; 6,294,989; 6,445,287; 6,472,979; 6,731,205and/or 7,423,522), and/or an ONSTAR® system, a compass, such asdisclosed in U.S. Pat. Nos. 5,924,212; 4,862,594; 4,937,945; 5,131,154;5,255,442 and/or 5,632,092, a control system, such as a control systemof the types described in PCT Application No. PCT/US10/38477, filed Jun.14, 2010 and published Dec. 16, 2010 as International Publication No. WO2010/144900, and/or any other accessory or circuitry or the like (withthe disclosures of the above-referenced patents and patent applicationsand PCT applications being hereby incorporated herein by reference intheir entireties).

The accessory or accessories may be positioned at or within a mirrorcasing of the interior rearview mirror assembly and may be included onor integrated in the printed circuit board positioned within the mirrorcasing, such as along a rear surface of the reflective element orelsewhere within a cavity defined by the casing, without affecting thescope of the present invention. The user actuatable inputs describedabove may be actuatable to control and/or adjust the accessories of themirror assembly/system and/or an overhead console and/or an accessorymodule / windshield electronics module and/or the vehicle. Theconnection or link between the controls and the systems or accessoriesmay be provided via vehicle electronic or communication systems and thelike, and may be connected via various protocols or nodes, such asBLUETOOTH®, SCP, UBP, J1850, CAN J2284, Fire Wire 1394, MOST, LIN,FLEXRAY™, Byte Flight and/or the like, or other vehicle-based orin-vehicle communication links or systems (such as WIFI and/or IRDA)and/or the like, depending on the particular application of themirror/accessory system and the vehicle. Optionally, the connections orlinks may be provided via wireless connectivity or links, such as via awireless communication network or system, such as described in U.S. Pat.No. 7,004,593, which is hereby incorporated herein by reference in itsentirety, without affecting the scope of the present invention.

Optionally, a display and any associated user inputs may be associatedwith various accessories or systems, such as, for example, a tirepressure monitoring system or a passenger air bag status or a garagedoor opening system or a telematics system or any other accessory orsystem of the mirror assembly or of the vehicle or of an accessorymodule or console of the vehicle, such as an accessory module or consoleof the types described in U.S. Pat. Nos. 7,289,037; 6,877,888;6,824,281; 6,690,268; 6,672,744; 6,386,742 and 6,124,886, and/or U.S.patent application Ser. No. 10/538,724, filed Jun. 13, 2005 andpublished Mar. 9, 2006 as U.S. Publication No. US-2006-0050018, whichare hereby incorporated herein by reference in their entireties.

Changes and modifications in the specifically described embodiments maybe carried out without departing from the principles of the presentinvention, which is intended to be limited only by the scope of theappended claims as interpreted according to the principles of patentlaw.

The invention claimed is:
 1. A method of calibrating cameras of a multi-camera vision system for a vehicle moving along a vehicle assembly line, said method comprising: moving a vehicle along a vehicle assembly line; equipping the vehicle as it moves along the vehicle assembly line with a plurality of cameras that includes (i) a front camera disposed at a front portion of the vehicle and having a field of view at least forward of the vehicle, (ii) a driver-side camera disposed at a driver side of the vehicle and having a field of view at least sideward of the vehicle, (iii) a passenger-side camera disposed at a passenger side of the vehicle and having a field of view at least sideward of the vehicle, and (iv) a rear camera disposed at a rear of the vehicle and having a field of view at least rearward of the vehicle; equipping the vehicle as it moves along the vehicle assembly line with an image processor for processing image data captured by the plurality of cameras; wherein, as the vehicle moves along the vehicle assembly line, a driver-side target at a driver-side region of the vehicle assembly line is viewed by (i) the front camera, (ii) the driver-side camera and (iii) the rear camera; wherein, as the vehicle moves along the vehicle assembly line, a passenger-side target at a passenger-side region of the vehicle assembly line opposite the driver-side region is viewed by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera; capturing image data by the plurality of cameras as the vehicle moves along the vehicle assembly line; detecting, via processing by the image processor of image data captured by the (i) the front camera, (ii) the driver-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the driver-side target at the driver-side region; detecting, via processing by the image processor of image data captured by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the passenger-side target at the passenger-side region; and as the vehicle moves along the vehicle assembly line, calibrating the plurality of cameras responsive to processing by the image processor of (i) image data of the driver-side target captured by the front, rear and driver-side cameras and (ii) image data of the passenger-side target captured by the front, rear and passenger-side cameras.
 2. The method of claim 1, wherein calibrating the plurality of cameras comprises first calibrating the front camera responsive to processing by the image processor of image data captured by the front camera of the driver-side target and the passenger-side target.
 3. The method of claim 2, wherein calibrating the plurality of cameras comprises calibrating the driver-side camera after calibrating the front camera, and wherein calibrating the driver-side camera is responsive to processing by the image processor of image data captured by the driver-side camera of the driver-side target, and wherein calibrating the plurality of cameras comprises calibrating the passenger-side camera after calibrating the front camera, and wherein calibrating the passenger-side camera is responsive to processing by the image processor of image data captured by the passenger-side camera of the passenger-side target.
 4. The method of claim 3, wherein calibrating the plurality of cameras comprises calibrating the rear camera after calibrating the driver-side camera and the passenger-side camera, and wherein calibrating the rear camera is responsive to processing by the image processor of image data captured by the rear camera of the driver-side target and the passenger-side target.
 5. The method of claim 1, wherein the driver-side target is disposed at a ground location at the driver-side region of the vehicle assembly line so as to be viewed by overlapping portions of the fields of views of the front camera and the driver-side camera as the vehicle moves along the vehicle assembly line, and wherein the passenger-side target is disposed at a ground location at the passenger-side region of the vehicle assembly line so as to be viewed by overlapping portions of the fields of views of the front camera and the passenger-side camera as the vehicle moves along the vehicle assembly line.
 6. The method of claim 5, wherein the driver-side target comprises a longitudinal line at the driver-side region that extends longitudinally along a direction that the vehicle is moving and the passenger-side target comprises a longitudinal line at the passenger-side region that extends longitudinally along the direction that the vehicle is moving, and wherein a plurality of tick marks extend laterally from the respective longitudinal lines.
 7. The method of claim 1, comprising, responsive to detecting the driver-side target and the passenger-side target, capturing and storing image data for an image data stitching computation.
 8. The method of claim 1, wherein calibrating the plurality of cameras comprises, via processing by the image processor of image data captured by the plurality of cameras, determining multi-axial misalignment of the plurality of cameras.
 9. The method of claim 8, wherein determining multi-axial orientation of the plurality of cameras comprises determining pitch, yaw and roll of each camera of the plurality of cameras.
 10. The method of claim 1, wherein calibrating the plurality of cameras comprises correction for lens distortion of a lens of each camera of the plurality of cameras.
 11. The method of claim 10, wherein correction for lens distortion of a lens of each camera of the plurality of cameras is based at least in part on lens nominal design data.
 12. The method of claim 1, wherein calibrating the plurality of cameras comprises determining a relationship between a degree of curvature of horizontal lines and vertical misalignment of a lens of each camera of the plurality of cameras to a center of an imager for each camera.
 13. The method of claim 1, wherein calibrating the plurality of cameras comprises correcting for angular and translational misalignment of the plurality of cameras.
 14. The method of claim 13, wherein correcting for angular and translational misalignment of the plurality of cameras utilizes a perspective correction that comprises a mathematical model of homographic transformation represented by a 3×3 matrix.
 15. The method of claim 1, wherein calibrating the plurality of cameras comprises an initial calibration process and, following the initial calibration process, fine tuning calibration to enhance image data stitching for images derived from image data captured by the plurality of cameras that are displayable at a display screen of the vehicle.
 16. The method of claim 1, comprising determining a degree of curvature of horizontal lines by detecting edges and points of the driver-side target and of the passenger-side target.
 17. A method of calibrating cameras of a multi-camera vision system for a vehicle moving along a vehicle assembly line, said method comprising: moving a vehicle along a vehicle assembly line; equipping the vehicle as it moves along the vehicle assembly line with a plurality of cameras that includes (i) a front camera disposed at a front portion of the vehicle and having a field of view at least forward of the vehicle, (ii) a driver-side camera disposed at a driver side of the vehicle and having a field of view at least sideward of the vehicle, (iii) a passenger-side camera disposed at a passenger side of the vehicle and having a field of view at least sideward of the vehicle, and (iv) a rear camera disposed at a rear of the vehicle and having a field of view at least rearward of the vehicle; equipping the vehicle as it moves along the vehicle assembly line with an image processor for processing image data captured by the plurality of cameras; wherein, as the vehicle moves along the vehicle assembly line, a driver-side target at a driver-side region of the vehicle assembly line is viewed by (i) the front camera, (ii) the driver-side camera and (iii) the rear camera; wherein the driver-side target is disposed at a ground location at the driver-side region of the vehicle assembly line so as to be viewed by overlapping portions of the fields of views of the front camera and the driver-side camera as the vehicle moves along the vehicle assembly line and viewed by overlapping portions of the fields of views of the driver-side camera and the rear camera as the vehicle moves along the vehicle assembly line; wherein, as the vehicle moves along the vehicle assembly line, a passenger-side target at a passenger-side region of the vehicle assembly line opposite the driver-side region is viewed by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera; wherein the passenger-side target is disposed at a ground location at the passenger-side region of the vehicle assembly line so as to be viewed by overlapping portions of the fields of views of the front camera and the passenger-side camera as the vehicle moves along the vehicle assembly line and viewed by overlapping portions of the fields of views of the passenger-side camera and the rear camera as the vehicle moves along the vehicle assembly line; capturing image data by the plurality of cameras as the vehicle moves along the vehicle assembly line; detecting, via processing by the image processor of image data captured by the (i) the front camera, (ii) the driver-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the driver-side target at the driver-side region; detecting, via processing by the image processor of image data captured by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the passenger-side target at the passenger-side region; as the vehicle moves along the vehicle assembly line, calibrating the plurality of cameras responsive to processing by the image processor of (i) image data of the driver-side target captured by the front, rear and driver-side cameras and (ii) image data of the passenger-side target captured by the front, rear and passenger-side cameras; and wherein calibrating the plurality of cameras comprises, via processing by the image processor of image data captured by the plurality of cameras, determining multi-axial misalignment of the plurality of cameras.
 18. The method of claim 17, wherein the driver-side target comprises a longitudinal line at the driver-side region that extends longitudinally along a direction that the vehicle is moving and the passenger-side target comprises a longitudinal line at the passenger-side region that extends longitudinally along the direction that the vehicle is moving, and wherein a plurality of tick marks extend laterally from the respective longitudinal lines.
 19. The method of claim 17, comprising, responsive to detecting the driver-side target and the passenger-side target, capturing and storing image data for an image data stitching computation.
 20. The method of claim 17, wherein determining multi-axial orientation of the plurality of cameras comprises determining pitch, yaw and roll of each camera of the plurality of cameras.
 21. A method of calibrating cameras of a multi-camera vision system for a vehicle moving along a vehicle assembly line, said method comprising: moving a vehicle along a vehicle assembly line; equipping the vehicle as it moves along the vehicle assembly line with a plurality of cameras that includes (i) a front camera disposed at a front portion of the vehicle and having a field of view at least forward of the vehicle, (ii) a driver-side camera disposed at a driver side of the vehicle and having a field of view at least sideward of the vehicle, (iii) a passenger-side camera disposed at a passenger side of the vehicle and having a field of view at least sideward of the vehicle, and (iv) a rear camera disposed at a rear of the vehicle and having a field of view at least rearward of the vehicle; equipping the vehicle as it moves along the vehicle assembly line with an image processor for processing image data captured by the plurality of cameras; wherein, as the vehicle moves along the vehicle assembly line, a driver-side target at a driver-side region of the vehicle assembly line is viewed by (i) the front camera, (ii) the driver-side camera and (iii) the rear camera; wherein the driver-side target comprises a longitudinal line at the driver-side region that extends longitudinally along a direction that the vehicle is moving, and wherein a plurality of tick marks extend laterally from the longitudinal line at the driver-side region; wherein, as the vehicle moves along the vehicle assembly line, a passenger-side target at a passenger-side region of the vehicle assembly line opposite the driver-side region is viewed by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera; and the passenger-side target comprises a longitudinal line at the passenger-side region that extends longitudinally along the direction that the vehicle is moving, and wherein a plurality of tick marks extend laterally from the longitudinal line at the passenger-side region; capturing image data by the plurality of cameras as the vehicle moves along the vehicle assembly line; detecting, via processing by the image processor of image data captured by the (i) the front camera, (ii) the driver-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the driver-side target at the driver-side region; detecting, via processing by the image processor of image data captured by (i) the front camera, (ii) the passenger-side camera and (iii) the rear camera as the vehicle moves along the vehicle assembly line, the passenger-side target at the passenger-side region; as the vehicle moves along the vehicle assembly line, calibrating the plurality of cameras responsive to processing by the image processor of (i) image data of the driver-side target captured by the front, rear and driver-side cameras and (ii) image data of the passenger-side target captured by the front, rear and passenger-side cameras; and wherein calibrating the plurality of cameras comprises correcting for angular and translational misalignment of the plurality of cameras.
 22. The method of claim 21, wherein calibrating the plurality of cameras comprises (a) calibrating the front camera responsive to processing by the image processor of image data captured by the front camera of the driver-side target and the passenger-side target, (b) calibrating the driver-side camera after calibrating the front camera, and wherein calibrating the driver-side camera is responsive to processing by the image processor of image data captured by the driver-side camera of the driver-side target, and wherein calibrating the plurality of cameras comprises calibrating the passenger-side camera after calibrating the front camera, and wherein calibrating the passenger-side camera is responsive to processing by the image processor of image data captured by the passenger-side camera of the passenger-side target, and (c) calibrating the rear camera after calibrating the driver-side camera and the passenger-side camera, and wherein calibrating the rear camera is responsive to processing by the image processor of image data captured by the rear camera of the driver-side target and the passenger-side target. 